Blender 2.78 cycles out of memory problem, in both cpu and gpu
If you sculpted, there's a high chance your face count is extremely high, and 8GB is not really that much ram. You can try to decimate the mesh (decimate modifier) and see if it will stop crashing and render with a lower poly count.

This will probably not be the accepted answer, but might help.

EDIT: If you are using subdivision, check that the view and render division levels are the same, since if you have a higher render number when you see it in the viewport its what you want, but when you render you get an exponential number of faces.